Novel aspects of taxifolin pharmacokinetics: Dose proportionality, cumulative effect, metabolism, microemulsion dosage forms.

Taxifolin (TFL) is a small drug molecule with a broad therapeutic potential limited by its poor aqueous solubility and excessive metabolism. Despite comprehensive research, some aspects of the TFL pharmacokinetics, e.g., dose proportionality and possible cumulative effect, remain unexplored. In the current study, we have tried to fill this gap. Our results revealed that the TFL pharmacokinetics in rats had nonlinear character in the dose range of 10-50 mg/kg after its single oral administration (AUC). For Cmax, the data are ambiguous: linearity was confirmed via the equivalence criterion and was disproved using the power model approach. Also, the cumulative drug effect was observed on the 4th day after its multiple-dose oral administration (25 mg/kg; compared to the 1st day). Interestingly, biologically active TFL metabolites such as aromadendrin and luteolin were putatively found in plasma samples, although they were previously detected only in feces. In addition, oil-in-water and water-in-oil microemulsions were fabricated to design novel drug delivery systems. These carrier dosage forms did not improve the TFL bioavailability but significantly affected its metabolism. To support pharmacokinetic studies, the bioanalytical liquid chromatography-tandem mass spectrometry method was developed and validated in the concentration range of 1-1000 ng/mL using candesartan as an internal standard. Liquid-liquid extraction with methyl tert-butyl ether was used to isolate the analytes from plasma followed by evaporation and reconstitution of the residues in acetonitrile. Thus, the present findings broaden our understanding of the TFL behavior in vivo and provide novel ideas and reference directions for its continued use in medical practice.

LC-MS/MS method for the determination of a semi-synthetic phenolic antioxidant 2,6-diisobornyl-4-methylphenol in rats after different administration routes.

IBP (2,6-diisobornyl-4-methylphenol) is a small drug molecule with antioxidant properties considered to be a promising neuro-, cardio-, and retinoprotective agent. In this study, a bioanalytical LC-MS/MS method for its determination in rat plasma was developed using 11H-indeno[1,2-b]quinoxalin-11-one oxime as an internal standard (IS). The analytes were extracted from plasma by liquid-liquid extraction technique using isopropyl alcohol:chloroform mixture (1:5, v/v) followed by evaporation and reconstitution of the residues in acetonitrile. The chromatographic separation was carried out on the EC Nucleodur C8 ec column (150 × 4.6 mm, 5 µm) under an isocratic elution mode using acetonitrile and water containing 0.1% (v/v) formic acid (97:3, v/v) as a mobile phase at a flow rate of 0.55 mL/min (40 °C). The IS and IBP were eluted at 3.79 ± 0.02 and 6.30 ± 0.02 min, respectively. The total analysis time was 7.00 min. Multiple reaction monitoring was used to conduct the MS/MS detection in the negative ion mode with transitions at m/z 245.9 â†’ 214.9 (IS) and 379.2 â†’ 256.0 (IBP). Validation studies of the developed method revealed good linearity over the range of 10-5,000 ng/mL. Within- and between-run accuracy was in the range of 92-110%, while within- and between-run precision was below 8%. Additionally, low matrix effects and high recovery (above 98%) were observed. IBP remained stable in rat plasma at room temperature for 4 h, at -80 °C for 21 days, over three freeze-thaw cycles, under vacuum concentrator (45 °C, dried residues) and auto-sampler (15 °C, processed samples) temperatures for 1 h and 24 h, respectively. Subsequently, the validated LC-MS/MS method has been successfully applied to quantitate IBP in actual plasma samples after a single oral, intramuscular, and subcutaneous dose of IBP (10 mg/kg in the peach oil) to rats. Pharmacokinetic studies show that more rapid and complete IBP absorption with a satisfactory excretion rate were observed after oral administration route compared to the intramuscular and subcutaneous ones.